A sealed package or bag placed in a box, referred to as a bag-in-a-box packaging, is conventionally used for applications such as cereal and cracker packaging. The bag acts as a moisture barrier to keep the contents of the bag fresh and the box provides stand up packaging for the shelf. The bag is usually heat sealed along the top and the bottom of the bag. The package is also heat sealed vertically along the center of the package, generally with a fin seal. The bag may be made from a film with a seal layer and a moisture barrier layer. When the bag is formed, the moisture barrier layer is positioned on the outer surface of the bag and the seal layer faces the interior of the bag.
FIG. 1 illustrates a conventional vertical form/fill/seal (“VFFS”) machine 10 which is used to form a bag from flat film 20. As shown in FIG. 1, the flat film 20 is wrapped around a filling tube 40 by a bag forming collar 50 and passes downward along the filling tube 40. The film 20 has a seal layer 22 that is positioned adjacent to the filling tube and a moisture barrier layer 24 that faces outward. As the film passes down the filling tube, the right edge 32 of the film is pressed against the left edge 34 of the film, so that the edges of the seal layer face each other. The edges 32, 34 are then folded over to lay flat against the filling tube and a longitudinal sealing device 60 runs along the film edges, forming a fin seal. The film is then advanced past the end of the tube, sealed at the bottom with cross sealing jaws 70, filled with contents and then sealed at the top with the same cross sealing jaws 70. A completed package with a fin seal is illustrated at FIG. 2.
Prior art films for cereal and cracker packaging generally include one surface that is heat sealable and another side that is heat resistant and provides a moisture barrier. The heat sealable surface seals easily to itself in a fin seal, while the heat resistant and moisture barrier layer does not melt on the longitudinal sealing device.
A disadvantage of this conventional method is that a fin seal requires excess film that is simply folded over and does not create volume in the bag. One approach to minimize the amount of film needed to make the package is to use a lap seal. A lap seal can save more than one inch of film along the length of the bag when compared to the film required to form a fin seal. A lap seal is illustrated at FIG. 2. In a lap seal, the inner surface of one edge is sealed to the outer surface of the other edge of the film.
As mentioned above, prior art bag-in-a-box with fin seals are made with a film having a heat sealable layer and a heat resistant layer. Other types of bags with lap seals have been formed from films with seal layers on both surfaces of the film. During the formation of a lap seal with such a film, the layer of the film that contacts a heat sealing device is a seal layer. The sealing device can melt the seal layer and may cause the film to stick to the sealing device. As a result, processing may need to be stopped or conducted more slowly to prevent buildup of film on the sealing device. In addition, the moisture barrier properties of the bag may be reduced because seal layers tend to be more permeable than barrier layers.
Another disadvantage of conventional bag in a box packaging is that the bag can be difficult to open, causing the package to tear instead of opening at the seal when a consumer attempts to open the package.